Grey snake-bark maple is a shrub that can grow into a tree with distinctive mottled, striped bark that resembles a snakeskin – hence the name. The alternative name of redvein maple is attributed to the red-brown color of the leaf veins. Like many maples, gray snake-bark maple hosts larvae of the Imperial moth. It also attracts pollinators such as bees.
I. Appearance and Characteristics
Acer rufinerve, the grey-budded snake-bark-maple, redvein maple or Honshū maple (Japanese: ウリハダカエデ urihadakaede, “melon-skin maple”), is a species of tree in the snakebark maple group, related to Acer capillipes (Kyushu maple). It is native to mountain forests of Japan, on Honshū, Kyūshū and Shikoku.
The Latin and English names rufinerve and “redvein” refer to the reddish down on the veins. The Japanese name urihadakaede (melon-skin) refers to the bark pattern.
It is a small deciduous tree growing to a height of 8–15 m, with a trunk up to 40 cm diameter. The bark on young trees is smooth, olive-green with regular narrow vertical pale green to greyish stripes and small greyish lenticels; on old trees, it becomes rough and grey.
The leaves are three-lobed (occasionally five-lobed with two additional small basal lobes), double serrated, 8–16 cm long and 6–16 cm broad, matt to sub-shiny dark green above, paler below with small tufts of rusty hair on the veins when young, becoming glabrous when mature; the petiole is greenish (rarely pinkish), 3–5 cm long. The leaves turn to bright orange or red in the autumn.
The flowers are produced in racemes 10 cm long, each flower 8–10 mm diameter, with five yellow to greenish-yellow sepals and petals; it is dioecious, with male and female flowers on separate trees.
The fruit is a paired samara 2–3 cm long with rounded nutlets.
It can be distinguished from the related Acer capillipes with which it often occurs, by the green petioles, the rufous hairs on the underside of the leaves (contrasting with the hairless or only thinly hairy A. capillipes leaves), and in flowering earlier in spring at the same time as the leaves appear.
This is one of the most commonly planted snakebark maples, and is a hardy, fast grower. It does not display much variation as a species but a notable cultivar is ‘Erythrocladum’ with yellow-green in both its leaves and the stripes of its bark. Variegated cultivars include ‘Albolimbatum’ and ‘Hatsuyaki’. ‘Winter Gold’ has bright golden-yellow bark.
II. How to Grow and Care
Sunlight
The grey snake-bark maple has a certain requirement for sunlight and prefers a partially shaded area. In cases of exposure to direct sunlight in the summer, the leaves of most varieties will wither, so shading is required. As the plants get older and their root system grows, this condition will be less of a problem. A few varieties will tolerate exposure to direct sunlight, such as ‘Beni Maiko’ and ‘De Shojo’. Some weeping varieties can also tolerate exposure to direct sunlight, such as ‘Ao Shidare’.
Sunlight conditions will directly affect the ornamental appearance of grey snake-bark maple leaves. In the spring, sufficient sunlight will make the maple leaves more vivid, while in cases of insufficient sunlight or partial shading the leaf color may fade. During the fall, sunlight can also affect the leaf color. For potted plants, full exposure to sunlight is recommended during the spring and the fall, with partial shading in the summer.
Temperature
The grey snake-bark maple has good cold resistance and is able to tolerate low temperatures. The grey snake-bark maple is native to the margins of forests in China, Japan, and North Korea, so these trees generally prefer a humid environment. Most grey snake-bark maple plants have shallow root systems, so they should be watered frequently during the summer. For some varieties, a sprayed mist should be provided during the summer to increase the humidity of the air around them.
Watering
Grey snake-bark maple is a plant that prefers a balance between moisture and dryness, reflecting its native habitat’s temperate climate. It requires watering once every 1-2 weeks to maintain optimal growth. This species displays an affinity for well-drained soil, indicative of its moderate water needs. As a deciduous tree, grey snake-bark maple’s water requirements decrease during dormancy in the colder months.
Soil
The grey snake-bark maple does not have many specific requirements for soil. It is a forest native, so it prefers well-drained soil that is rich in humus and slightly acidic. Its main root will extend deep into the soil, but its tiny fibrous roots will be concentrated near the soil surface, so accumulated water in the soil tends to cause root rot.
Fertilizing
Potted seedlings should be given slow-release fertilizer only. For seedlings grown in gardens, fertilizer should be applied three times a year: once in the early spring, once in early summer for the growth period, and once in the fall.
Planting Instructions
The best time for planting or transplanting a grey snake-bark maple is following defoliation in the fall. At this time, the leaves will have fallen off so there is little transpiration and water loss can be avoided. In addition, the root system will still be growing at this time, preparing for regrowth the following spring. Transplanting should be avoided on the coldest days because cold wind can kill some of the shoots and branches. During the winter, in areas that cannot be sheltered from the wind, it is recommended to cover the branches.
Pruning
Pruning is mainly used to enhance internal ventilation, improve shoot formation, promote growth, and for shaping. The common approach to pruning is to remove any old or weak branches, remove any branches that disrupt the shape of the tree, and remove any branches that cross other branches. Pruning is used to control the plant according to the required height and shape. Generally, this follows the “Y-type” pruning method.
It is possible to prune a gray snake-bark maple throughout the year, but the coldest winter months should be avoided to prevent damage to the plant. Major pruning to shape a maple can be performed following defoliation in the fall, or prior to leaf growth in the spring. It is recommended to prune in the fall because withered and full buds can be easily distinguished.
According to the shaping plan, you can prune any withered buds and keep the full ones, thus making your tree healthier. For pruning in the summer, diseased, weak, or dead branches can be removed, mainly to enhance the tree’s ventilation.
If grown as a potted plant, the roots can easily occupy the entire flowerpot due to the limited space. This can make a grey snake-bark maple prone to aging if an old flowerpot is not changed. It is recommended that old roots are pruned during the dormancy period, that is, cut off any old, coarse, diseased, and weak roots.
Propagation
Common propagation methods include grafting, taking cuttings, and sowing seeds.
Grafting is the most common propagation method. Seedlings of Acer palmatum or Acer oliverianum are usually selected for the rootstock. Grafted seedlings have strong roots and grow rapidly, but poor affinity is occasionally present in some cases. Seedlings with Acer oliverianum as the rootstock are less hardy.
Cuttings take longer to grow and are mostly used in the production of bonsai.
Sowing seeds is a common way to cultivate new varieties. The hybrid offspring of two different maples are sown and valuable individuals are then selected from the seedlings. The traits of the parents may not be maintained in the selected offspring.
